Many devices on the market have been developed to be handled by persons that are not trained medical staff. Such devices have to be very simple and intuitive to use. Therefore, many devices have been arranged with a number of automatic functions, such as penetration, injection, withdrawal, shielding of the medicament delivery member, etc.
A device that has been on the market for some time is disclosed in WO2005044348A1. It comprises an auto injector having a number of automatic features that render the device easy and intuitive to use. A main drive spring is used for first performing a penetration sequence, followed by a dose delivery sequence. The device is arranged with a two-step function in that a needle shield has to be pressed against a dose delivery site in order to unlock activation of the device. That is, the movement of the needle shield in the distal direction inside the device will unlock an actuator function that can be activated by an actuator button. When the dose delivery has been performed and the device is removed from the dose delivery site, a needle shield spring acts on the needle shield for covering the injection needle after use. The needle shield spring also acts to lock the actuator function again, should the device be removed from the dose delivery site before activation.
For some types of drugs, the device requires a stronger drive spring than originally developed for the device. However, a stronger drive spring has resulted in some functional issues due to increased friction between parts, which is due to the increased force from the drive spring. In some instances, the needle shield has not been able to overcome the increased friction, causing the actuator function to remain unlocked if the device is removed from the dose delivery site before activation. In such a situation the device may be unintentionally activated if the actuator button should be operated without the device being pressed against a dose delivery site.